If all you really wanted was a table of sigma values, then:
Table[sigma[alpha[i]], {i, 100}]
If you want both alpha and sigma, then
alphaTable = Table[alpha[i], {i, 100}]
sigmaTable = Map[ sigma, alphaTable ]
You can even use the Greek characters \alpha and \sigma, but that
doesn't post well on MathGroup.
Daniel